An image forming apparatus having an image correction function for correcting a formed image position or an image forming density is known. In such an image forming apparatus, an amount of mismatch related to the formed image position or density is measured and the formed image portion or density is corrected such that the measured amount of mismatch decreases. Although frequent image corrections can maintain an image quality, they may cause inconveniences for a user, such as a long waiting time or an increased consumption of ink or toner.
From that point of view, in the known image forming apparatus, a variation in printed page count or elapsed time since the last image correction is obtained and an amount of mismatch is measured when the variation exceeds a reference value. When the certain number of pages is printed since the last image correction, a certain amount of mismatch is expected due to abrasions or vibrations of parts caused by printing operation. Conditions to determine whether the image correction is required are usually predefined so that a required image quality can be maintained even when the maximum amount of mismatch within an estimated rage is measured.
The conditions are defined based on an estimation that the maximum amount of mismatch is measured. If the estimated amount of mismatch is significantly different from an actual amount of mismatch, the image correction may be performed frequently even the actual amount of mismatch is too small to affect the image quality. Namely, unnecessary image corrections may be performed. The same problem occurs in the image forming density corrections.